Compound Interest Calculator
See how savings or investments grow with compound interest — set a principal, rate, term and monthly top-up. Free and private.
Your savings plan
- Final balance
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- Total contributions
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- Total interest earned
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How to use
- Enter your starting principal, the annual interest rate and how many years you plan to save or invest.
- Choose how often the interest compounds — annually, semi-annually, quarterly, monthly or daily — and add a regular monthly contribution if you make one.
- Read the final balance, your total contributions and the interest earned. Everything updates as you type, and Calculate confirms the latest figures.
FAQ
How is the future value worked out?
The principal grows by the standard compound-interest formula A = P × (1 + r ÷ n) raised to the power n × t, where r is the rate as a decimal, n is how many times a year interest compounds, and t is the number of years. Any regular monthly contributions are grown separately as a monthly annuity and added on top, so both your lump sum and your top-ups earn interest.
Does the monthly contribution earn interest too?
Yes. Each monthly contribution starts earning interest from the month you add it, using a monthly rate of the annual rate divided by twelve. Earlier contributions have more time to grow, which is why the total interest can be much larger than the interest on the principal alone.
Is anything sent to a server?
No. Every figure is plain maths done in your browser, so the amounts you type are never uploaded. The calculator works offline and keeps your numbers completely private. Results are estimates and do not include tax or fees.